If the page actually exists (remember, in any given second, a few thousand new web pages begin to exist and another few thousand disappear - there are trillions [at least] of web pages) and the browser is showing it as "not available", not as 404 or "not found", it's due to transient conditions on the path from the phone to the page - including the DNS server the phone is using, which could be different for 2 phones in the same room. If the error is 404 or "page not found", it's possible that the server just couldn't find the file you told it you wanted. (A "page" is a file [or more, but at least one].)
Or it could be just another bug in Lollipop. They'll eventually get to it, or they'll release 6.0, whichever comes first. Eventually, the marketing department will be told that the development department starts issuing release dates again. (When you have to release software on some other department's schedule - a department with people who have no idea how software gets "done" - you release buggy software. Always. You can't release bug-free software if you announce the release date before the release date. [Once the last bug is fixed, you can release the software. Five minutes earlier, you had no idea when it would be ready for release. Even if you absolutely know, with not a shred of doubt, that it'll be ready tomorrow, you risk bugs if you announce the release date as tomorrow. They can find a major, but until now not seen, bug tomorrow morning - and take 6 months to figure out hat's causing it.])
So how to fix your problem? First find out why it's happening - that's how you fix all software problems. Whether you find it, Google finds it or someone else finds it, someone has to find the cause. "It doesn't work" doesn't help fix it. So no answer at this time. There are lots of things you can try, but that's like rapidly spinning around on a turntable, blindfolded, and throwing darts at a tiny target no one gave you a clue to the position of. You might get a dart in the target (and you only need one in this case), but the odds of finding the winning lottery ticket floating in the middle of the Atlantic are probably better.